Yemen's Iranian-allied Houthi rebels have released videos made by their fighters before they were killed in action that highlight the sectarian nature of a conflict that risks descending into all-out civil war.

The Shi'ite Muslim group seized the capital Sana'a and much of the north in September and have since battled with Sunni tribesmen backed by al Qaeda militants in Yemen's central mountains, fighting in which dozens of people die every week.

Sixteen videos posted online by the Houthi channel al-Masira in an apparent bid to boost morale show bearded fighters in green headbands brandishing rifles, urging obedience to their leader Abdel Malik al-Houthi and praising death in the cause of "holy war''.

"This is my message to the enemies of the Islamic nation: we are prepared to face you, God willing, and God aids us. I ask Him to grant us martyrdom for his sake,'' says Yahya Abdullah al-Thaan, described by a subtitle as a "martyr''.

"May our prayers be upon Mohammed and his pure family,'' he adds, invoking a Shi'ite religious formula. "God is Great, death to America, death to Israel, curse upon the Jews, victory to Islam!''

Houthi officials did not immediately respond to Reuters' request for comment on the videos.

The clips have the florid style and high production values of other Iran-linked militant groups in the region such as Palestinian Hamas and Lebanese Hezbollah.

The United States and Yemen's Sunni Gulf neighbors have watched the Houthi advance with grave concern, believing Iran seeks regional sway through powerful militias in Lebanon, Syria, Iraq and now Yemen.

Yemen's president and defense minister have fled to the southern port city of Aden and set up a Gulf-backed rival administration there, while the north drifts closer to Iran.

Houthi authorities in Sanaa this month signed a civil aviation agreement with Tehran for 14 weekly flights between the two capitals, and a Houthi politician who used to head Yemen's branch of Iran's pan-Arab news channel Al-Alam was appointed chief of state television over the weekend.